In recent years, in a manufacturing process of a semiconductor device, a method called chemical oxide removal (COR) in which chemical etching is performed without generating plasma within a chamber draws attention as a method capable of performing miniaturization etching substituted for plasma etching.
As the COR, there is known a process in which an SiO2 film is etched by allowing a hydrogen fluoride (HF) gas and an ammonia (NH3) gas to be adsorbed to a silicon oxide film (SiO2 film) existing on a surface of the semiconductor wafer as a process target within a chamber held in a vacuum, causing the gases to react with the silicon oxide film to generate ammonium fluorosilicate ((NH4)2SiF6; AFS), and sublimating the ammonium fluorosilicate by heating the same in a subsequent step.
On the other hand, in a manufacturing process of a semiconductor device, a chemical vapor deposition-based (CVD-based) SiO2 film formed by a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method may be used as an SiO2 film that is an etching target. In this case, since there may be a case where the CVD-based SiO2 film adjoins a thermally-oxidized film of SiO2 formed by thermally oxidizing silicon or a silicon nitride (SiN) film, it is required to etch the CVD-based SiO2 film at a high selection ratio with respect to the thermally-oxidized film and the SiN film.
Moreover, a native oxide film is formed on the surface of the semiconductor wafer by natural oxidation of Si-based material and thus it is required to only etch the native oxide film while the thermally-oxidized film or the SiN film existing on the semiconductor wafer is etched as less as possible, so as to remove the native oxide film.
However, when an HF gas and an NH3 gas are used as the etching gas as in the related art, it is difficult to etch the CVD-based SiO2 film or the native oxide film at a sufficient selection ratio with respect to the thermally-oxidized film and the SiN film.